1. Field of the Invention
The present invention relates to a motilin-like polypeptide, namely a polypeptide having a pharmacological activity similar to motilin, a salt thereof, a process for the preparation of the polypeptide, a recombinant DNA thereof, and a plasmid for expressing the polypeptide as well as a use of the polypeptide for curing gastroenteropathies.
2. Related Arts Motilin is one of peptide hormones, first isolated from mucous membrane of porcine upper small intestine, and its amino acid sequence determined by Brown J. C. et al ["Gastroenterology", Vol. 62, pages 401-404 (1972) and "Can. J. Biochem.", Vol. 52, pages 7-10 (1974)]. The porcine motilin consists of 22 amino acids and has a molecular weight of about 2700.
While, some of the present inventors have succeeded in isolation of cloned cDNA encoding human motilin precursor, the nucleotide sequence therein including a part designating the amino acid sequence same with that for the porcine motilin, so that it has been made apparent that the human motilin has the amino acid sequence same with that for the porcine motilin [Jap. Pat. No. Sho 63-276489(A) which corresponds to U.S. patent application Ser. No. 07/190,849 and European Pat. Appln. No. 88107108.81].
As physiological activities of the motilin, a hypermotility action of digestive tract and contracting action of gastroduodinal and colonic smooth muscle therein have been well known. As the hypermotility action, it has been reported that the rate of gastric emptying is shortened ["Gastroenterology", Vol. 80, pages 456-460 (1981)] and as the contracting action of smooth muscle in the digestive tract, it has been known that the motilin shows a strong contracting action to a rabbit and human gastrointestinal tract, independing from a neuro system. Moreover, no report has been issued on any specific side-effect. Therefore, it has been considered that the motilin is useful for curing gastroenteropathies at the period of post-operation and for diagnosis thereof. In connection with this, please note that prostagrandin has widely been employed for curing the gastroenteropathies, although the drug shows a relatively strong side-effect.
It has also been reported that chemically synthesized motilin analogue-methionine residue at 13-position of motilin being substituted with leucine or norleucine residue- shows biological activity similar to pure native porcine motilin ["Scand. J. Gastroenterology", Vol. 11, pages 119-203 (1976) and others]. Therefore, it has been considered that methionine residue at 13-position has almost no influence on useful activity of the motilin.
The motilin according to widely accepted technical art has been obtained through an extraction from porcine organ tissue and thus it was quite difficult to obtain the same in large amount. Since the motilin is a polypeptide consisting of 22 amino acids, a large scale production is difficult and a cost thereof becomes higher, even if a chemical synthesis shall be applied therefor. Namely, the motilin has not actually been employed for clinical use, due to its poor productivity, in spite of that an effectiveness thereof as the drug for curing gastroenteropathies has been expected.
Therefore, various studies have been made for preparing polypeptides having motilin-like biological activity, with a reasonable cost, by utilizing the so-called "Biotechnology" [Jap. Pat. Nos. Sho 63-71195(A) and 63-208006(A)].
Further, such studies have also been made to develop motilin analogues showing biological activities higher than those of the motilin per se [Jap. Pat. No. Sho 61-26559(B)].
All of said processes utilizing the Biotechnology comprise a step for cleaving a polypeptide chain with use of cyanogen bromide, and a step for removing an excess peptide chain containing homoserine at C-terminal, with use of an enzyme. However, the enzymatic treatment reduces yield of a desired motilin analogue to increase a cost thereof, which makes difficult a large scale production of the motilin analogue.